feat: Optimize Makefile for Improved Performance and Usability

[cubxxw]

Key Changes

• Immediate Variable Assignment: Changed VETPACKAGES and GOFILES to use immediate assignment (:=) to avoid re-evaluation of shell commands on each reference, enhancing performance.
• Simplified fmt Command: Updated the fmt target to format all Go files in the project directory at once instead of individually. This approach is not only more efficient but also simplifies the command.
• Unified VETPACKAGES Usage: Standardized the exclusion of /vendor/ and /examples/ directories across both the vet and test targets to maintain consistency and reduce redundancy.
• Added all Target: Introduced an all target as the default when running make without specific targets. This target sequentially runs fmt, vet, and test, providing a comprehensive check with a single command.
• Introduced help Target: Added a help target that dynamically generates a help message from comments in the Makefile. This feature aids new users and contributors by providing quick access to target documentation.